1. Field of the Invention
The present invention relates to a plasma processing apparatus, and particularly, to a plasma processing apparatus such as a plasma CVD apparatus or a plasma etching apparatus or the like.
2. Description of the Related Art
An example of the conventional plasma processing apparatus will be explained below by referring to FIGS. 9 and 10. This example shows an inductively coupled plasma processing apparatus. The inductively coupled plasma processing apparatus includes a plasma generating mechanism having an electric discharge chamber 51 made of a dielectric material and an annular antenna
In the plasma processing apparatus shown in FIG. 9, there is the above-mentioned annular antenna 52 for introducing radio-frequency electric power into the electric discharge chamber 51. A plasma diffusion chamber 53 is provided under the electric discharge chamber 51 so as to connected with the chamber 51, which is made of a metallic material. A not-illustrated reactive gas introducing mechanism supplies a reactive gas to the electric discharge chamber 51 and further the internal pressure thereof is reduced to 100 Pa or lower. Furthermore, when the annular antenna 52 supplies the radio-frequency electric power, electric discharge occurs in the electric discharge chamber 51 and thereby plasma can be generated. This reactive gas introducing mechanism is well known. Active species included in the plasma diffuse from the electric discharge chamber 51 into the plasma diffusion chamber 53. The active species process the surface of a substrate 55 placed on a substrate holding mechanism 54 in the plasma diffusion chamber 53.
As shown in FIG. 10, a plurality of magnetic circuit sections 56 are arranged at the outer periphery of the plasma diffusion chamber 53 at almost equal intervals. Each of the magnetic circuit sections 56 includes a yoke 57 for forming a magnetic path and two rod-shaped permanent magnets 58 secured to the yoke 57. A plurality of rod-shaped permanent magnets 58 are parallel with the central axis of the plasma diffusion chamber 53 and arranged in pairs which are arranged at equal intervals, and further all of them contact the outside of the plasma diffusion chamber 53. Polarities of adjacent magnets of the plural permanent magnets 58 are different from each other. The magnetic circuit sections 56 generate a magnetic field referred to as "a line cusped magnetic field" along the inside of the plasma diffusion chamber 53. The magnetic circuit sections 56 generate lines of magnetic flux 59 near to the inside of the plasma diffusion chamber 53 and along the inside thereof. The lines of magnetic flux 59 in the plasma diffusion chamber 53 capture charged particles such as electrons and ions in the plasma. Therefore, the number of charged particles colliding with the inside surface of the plasma diffusion chamber 53 is decreased and therefore the number of charged particles which are deactivated is reduced. Therefore, the plasma can efficiently be maintained in the plasma diffusion chamber 53. The lines of magnetic flux 59 generated in the plasma diffusion chamber 53 are referred to as "a bucket magnetic field".
In the conventional plasma processing apparatus shown in FIGS. 9 and 10, a film deposited on the inside of the plasma diffusion chamber 53 produces particles causing contamination. The deposited film causes a problem that the reproducibility of the plasma generated by the plasma generating mechanism is deteriorated. Therefore, the film deposited on the inside of the plasma diffusion chamber 53 has a bad effect on the reproducibility of the plasma processing. To solve this problem, the plasma diffusion chamber 53 is conventionally heated for the plasma processing so that the film is not deposited on the inside of the plasma diffusion chamber 53. Further, a problem solving method has been reported, in which a relative percentage of necessary active species in plasma can be increased by raising the temperature of the inside of the plasma diffusion chamber 53 (e.g. Sugai et al., 41st OYOBUTSURIGAKU KANREN RENGO KOENKAI YOKOSHU Second Separate Volume, p. 536). According to this report, it is estimated that temperature control of the plasma diffusion chamber 53 is an important factor to optimize the plasma processing.
However, since the above conventional apparatus is provided with the magnetic circuit sections 56 contacting the outside of the plasma diffusion chamber 53 in order to efficiently maintain the plasma, the temperature of the magnets 58 of the magnetic circuit sections 56 also rises as the temperature of the plasma diffusion chamber 53 is raised. When the temperature of the magnets 58 rises, demagnetization occurs in comparison with a state thereof at room temperature. Therefore, in the plasma diffusion chamber 53 which has been heated, the plasma confining effect based on the magnetic circuit sections 56 is decreased. By cooling the magnets 58 provided to the plasma diffusion chamber 53 to solve the problem, the temperature of portions of the plasma diffusion chamber 53 corresponding to the magnets 58 is lowered. Accordingly, the temperature of the inside of the plasma diffusion chamber is non-uniformed and thereby films are locally deposited on the inside thereof to cause contamination particles. This is a problem.